The objective of the proposed research plan is to study the mechanism by which heparan sulfate proteoglycans synthesized by endothelial cell cultures interact with certain proteins (blood factors) and inhibit their enzymatic activity. To this end, the heparan sulfate proteoglycans that are released into the supernatant growth medium will be isolated and characterized by various biochemical techniques, including the analysis of the structural features of the glycosaminoglycan chains with the use of various degradative enzymes and the elucidation of the primary structure of the protein core.